Messages in this thread | | | Date | Thu, 11 Nov 2021 00:39:52 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH v3 01/16] perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and deref |
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On Wed, Nov 10, 2021, Paolo Bonzini wrote: > On 11/4/21 15:18, Sean Christopherson wrote: > > If I'm interpeting Paolo's suggestion > > correctly, he's pointing out that oustanding stores to the function pointers in > > @cbs need to complete before assigning a non-NULL pointer to perf_guest_cbs, > > otherwise a perf event handler may see a valid pointer with half-baked callbacks. > > > > I think smp_store_release() with a comment would be appropriate, assuming my > > above interpretation is correct. > > > > Yes, exactly. It should even be rcu_assign_pointer(), matching the > synchronize_rcu()
And perf_guest_cbs should be tagged __rcu and accessed accordingly. Which is effectively what this version (poorly) implemented with a homebrewed mix of {READ,WRITE}_ONCE, lockdep(), and synchronize_rcu().
> in patch 1 (and the change can be done in patch 1, too).
Ya, the change needs to go into patch 1.
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